The invention relates to submersible pumps actuated particularly by hydraulic engines, wherein therefore it is necessary to control, besides the leaks of the pumped fluid, also those of the driving fluid and further the unavoidable mixing of the driving fluid with the pumped fluid in the above leaks.
It is known that the greatest danger in the operation of said pumps is that of a mixing of the pumped fluid with the driving fluid, either during the operation of the pump or during the rest periods thereof.